1. Field of the Invention
The present invention is generally related to stimulating nerves and body parts. More specifically, the present invention is related to nerve stimulation patches used for stimulating nerves and body parts to achieve therapeutic results.
2. Description of the Related Art
Nerves are part of the peripheral nervous system of a human body. They convey sensory signals back and forth from the skin and body organs to the central nervous system. Nerves may become damaged due to wear and tear, physical injuries, infection, and/or the failure of the blood vessels surrounding the nerves. These functional defects may be accompanied by pain, numbness, weakness, and in some cases, paralysis. Other problems resulting from damaged nerves may include urinary and fecal incontinence.
Different tactics have been developed to treat the above-mentioned problems. For example, treating urinary incontinence may involve behavior modification such as urinating more frequently and wearing protective undergarments. In certain social situations, however, individuals may not be able to follow the practice of frequent urination or wearing protective undergarments. Another approach involves a medical therapy including taking prescribed drugs. This methodology may result in adverse side effects or drug interactions, however, that will ultimately require discontinuation.
Another technique for treating the above-mentioned conditions involves stimulating a nerve using an electro-medical device that is positioned near a target nerve. One such electro-medical device is commonly referred to as an Implantable Pulse Generator (IPG). An IPG typically includes one or more electrodes, an electrical pulse generator, a battery, and a housing. The electrical pulse generator generates an electrical signal adapted to stimulate a target nerve. When the electrodes receive the signal from the generator, they draw energy from the battery and generate an electric field of suitable strength to stimulate the target nerve.
IPG's have proven to be somewhat effective for stimulating nerves, however, they are extremely invasive because they must be implanted inside a patient's body during a surgical procedure. IPG's also consume a significant amount of power, which may be due to an increase in electrical impedance between the electrodes, or an increase in electrical impedance between the electrodes and the IPG. This may happen due to several factors such as electrode migration, encapsulation of one or more electrodes, and material property changes in the electrodes or body tissue. Material property changes in the electrodes may occur due to a number of factors including chemical changes caused by body fluids being present at the surface of the electrodes, frequent passing of electrical current through the tissue, and normal wear and tear occurring during daily activities.
Higher battery power consumption may also be caused by a phenomenon referred to as “desensitization of stimulus,” whereby the human body responds to an applied external charge by offering a resistance to the applied external charge. The body resists the applied external charge by increasing the stimulation threshold for a target nerve, thereby rendering the earlier stimulus level ineffective. To overcome this problem, a more powerful charge must be generated, which consumes even more battery power. This requires frequent replacement and/or recharging of the batteries.
In some nerve stimulation devices, it has been observed that the generated electric field spreads widely, affecting untargeted muscles and nerves along with the target nerve. The wide spreading of the electric field significantly reduces the strength of the electrical signal at the target nerve. In order to properly stimulate the target nerve, the strength of the electrical signal must be substantially increased. This requires the devices to draw more power from the battery.
There have been a number of efforts seeking to stimulate nerves in a more efficacious and non-invasive manner. For example, non-invasive techniques for treating the above conditions are disclosed in commonly assigned U.S. Patent Publication Nos. 2005/0277998, filed Jun. 7, 2005, and US 2006/0195153, filed Jan. 31, 2006, the disclosures of which are hereby incorporated by reference herein. Specifically, in one or more embodiments thereof, the '998 publication teaches a non-invasive, transcutaneous neurostimulation device that generates and transmits a controlled, amplitude-modulated waveform comprising a carrier signal and a pulse envelope. The carrier waveform is designed to be of sufficient frequency to overcome attenuation due to tissue impedances. The pulse envelope contains specific pulse width, amplitude and shape information designed to stimulate specific nerves.
FIGS. 1 and 2 show a conventional nerve stimulating device 20 including a first layer 22 having a top surface 24 and a bottom surface 26. The bottom surface 26 of the first layer 22 is covered by an adhesive layer 28 having openings 30A, 30B extending therethrough that accommodate active and return integrated electrodes 32A, 32B. The adhesive layer 28 includes the holes that accommodate the shape of the electrodes 32A, 32B and allow direct contact of the electrodes with the surface of a patient's skin. The device 20 includes electrolyte pads 34A, 34B that cover the respective electrodes 32A, 32B. The electrodes 32A, 32B may be secured directly to the first layer 22, or may be held in place by a second layer comprised of any suitable material such as a plastic. The integrated electrodes may be gold-plated or other corrosion-resistant electro-deposited metal pads for the connection to the electrolyte for the stimulating electrode. The device includes a third layer 36 of a flexible electronics board or flex board that contains all of the electronic elements described in the '998 publication and that is electrically coupled to the electrodes 32A, 32B. The flex board 36 has parts that are folded over the batteries to complete battery connections and to nest the electronic components into a more compact space. A fourth layer is a thin film battery 38 of any suitable size and shape that can be held in place by a battery seal or ring 40, and the top cover 42 is any suitable covering such as the plastic coverings commonly used in bandages.
Referring to FIG. 2, the nerve stimulating device 20 includes a photodiode 44 underlying a section of the top layer, which can be used as an extremely low-power communication receiver. The photodiode is small, inexpensive, consumes zero power when inactive, and is much more energy and space-efficient than an RE link. The device 20 includes electrodes 32A, 32B powered by batteries 38A, 38B, which are surrounded by battery seals 40A, 40B. The two stimulation electrodes 32A, 32B are shifted off to one side, resulting in a somewhat D-shaped device. The top cover 42 is water resistant for protecting the internal components during typical activities such as washing, bathing and showering.
In spite of the above advances, there remains a need for improved devices and methods of stimulating body parts and nerves. In particular, there remains a need for selective nerve stimulation patches that are more compact and have a smaller footprint, that are more economical, that have less parts, and that are easier to assemble. There also remains a need for improved nerve stimulation devices that effectively stimulate target nerves and body parts, while not stimulating untargeted nerves and body parts. Furthermore, there remains a need for nerve stimulation devices that are less invasive, and that require less power to operate effectively, thereby minimizing the need to replace and/or recharge power sources.